Neoproterozoic banded iron formations (BIF) and ironstones occur in the Urucum mining district (Pantanal, Brazil). Microbially mediated formation as microbialites has been proposed for these deposits. This study aims to provide a high resolution characterization of micro-textural features, mineral assemblage and distribution to gather evidence for two microbial ore forming systems: Fe- and Mn-oxidizing metabolic processes and cyanobacterial activity Optical- and cathodoluminescence rock microscopy, Fourier Transform Infrared (FTIR), and Raman spectroscopy allowed the identification of syngenetic and diagenetic minerals. Evidence from BIF and nodule samples points to low temperature, suboxic, neutral/slightly alkaline formation conditions, but rarely diagenetic acidic and anoxic local conditions occurred. Direct evidence for the action of microorganisms is: (a) microtextural evidence of microbially mediated formation of the ore beds, which occur as microbialites; (b) mineral types of syngenetic origin (ferrihydrite, todorokite, manganite) with various types of organic matter incorporated, (c) light isotope signal (cited negative hematite δ⁵⁷Fe) and; (d) mineralized sedimentation cycles of Fe, Mn, Ca and Si. Two microbial ore forming systems are proposed as dual systems, characterized by the main Fe- and Mn-oxidizing metabolic processes and intense cyanobacterial activity. More ordered minerals, such as hematite, goethite and anatase, formed during diagenesis of Fe-rich biomat. Calcite-type (calcite, Mn-calcite, rhodochrosite) and dolomite-type carbonate structures (kutnohorite, ankerite, dolomite) occurred. Fine-grained carbonate is the common constituent, with some idiomorphic occurrences and dissemination in the laminae and nodules. The composition of the ankerite and the other carbonates is highly variable. The BIF’s gray laminae consist of hematite-rich part with minor quartz, scarce carbonate and apatite. The red laminae contain high contents of carbonate and hematite, with quartz and further diagenetic minerals (feldspar, apatite). Hematite occurs in considerable amount, but it is enough only for turning jasper reddish in color. Nodules were segregated from laminae by diapirism and/or microbial activity and underwent the same syngenetic and diagenetic changes as the microlayers from which they are segregated. Nodule compositions fit well with the diagenetic trends common in such ore forming systems. Most likely the differences between laminae and nodules are consequences of different initial organic matter contents and fine alternation of the oxygen supply of the system.

新元古代带状铁地层 (BIF) 和铁矿石出现在乌鲁库姆矿区（巴西潘塔纳尔湿地）。微生物介导的形成如微生物岩已被提议用于这些矿床。本研究旨在提供微观结构特征、矿物组合和分布的高分辨率表征，以收集两种微生物成矿系统的证据：Fe 和 Mn 氧化代谢过程和蓝藻活性光学和阴极发光岩石显微镜，傅里叶变换红外(FTIR) 和拉曼光谱可以鉴定同生和成岩矿物。来自 BIF 和结核样品的证据表明，低温、低氧、中性/微碱性地层条件，但很少发生成岩酸性和缺氧的局部条件。微生物作用的直接证据是： (a) 微生物介导的矿床形成的微观结构证据，矿床以微生物岩的形式出现；(b) 同生成因的矿物类型（水铁矿、铁镁矿、锰铁矿），掺入了各种类型的有机物，（c）轻同位素信号（引用负赤铁矿 δ⁵⁷Fe) 和; (d) Fe、Mn、Ca 和 Si 的矿化沉积循环。提出了两种微生物成矿系统作为双重系统，其特征是主要的铁和锰氧化代谢过程和强烈的蓝藻活动。更有序的矿物，如赤铁矿、针铁矿和锐钛矿，是在富铁生物垫成岩过程中形成的。出现方解石型（方解石、锰方解石、菱锰矿）和白云石型碳酸盐结构（kutnohorite、ankerite、白云石）。细粒碳酸盐是常见的成分，在纹层和结核中有一些自形产状和散布。ankerite 和其他碳酸盐的组成变化很大。BIF 的灰色薄层由富含赤铁矿的部分和少量石英、稀有的碳酸盐和磷灰石组成。红色薄层含有高含量的碳酸盐和赤铁矿，石英和其他成岩矿物（长石、磷灰石）。赤铁矿的含量相当可观，但仅用于将碧玉变成红色就足够了。结核通过底辟作用和/或微生物活动与薄片分离，并经历了与分离它们的微层相同的同生和成岩变化。结核组成与此类成矿系统中常见的成岩趋势非常吻合。薄片和结核之间的差异很可能是不同初始有机物含量和系统供氧的精细交替的结果。结核通过底辟作用和/或微生物活动与薄片分离，并经历了与分离它们的微层相同的同生和成岩变化。结核组成与此类成矿系统中常见的成岩趋势非常吻合。薄片和结核之间的差异很可能是不同初始有机物含量和系统供氧的精细交替的结果。结核通过底辟作用和/或微生物活动与薄片分离，并经历了与分离它们的微层相同的同生和成岩变化。结核组成与此类成矿系统中常见的成岩趋势非常吻合。薄片和结核之间的差异很可能是不同初始有机物含量和系统供氧的精细交替的结果。